Much effort has been put into the development of secure lock cylinders. Various pin and tumbler arrangements have been devised to resist picking and other attacks. However, a lock cylinder is no more secure than the housing into which it is mounted, and the means employed to mount the lock within the housing.
Prior art techniques for mounting lock cylinders in locks are shown in FIGS. 1 and 2. In FIG. 1, a lock cylinder 10 is received in a cavity formed by walls 12 that extend back from the face plate 14. A pin 16 on the back of the lock cylinder 10 engages a bolt 18 and serves to extend or retract the bolt.
While relatively secure at the back, the front of the FIG. 1 lock cylinder is held in place only by a swaged cover member 20 that is force-fit into an opening in the front of the face plate 14. This lock can be jimmied simply by prying out the swaged cover member 20, permitting removal of the lock cylinder 10 and free manipulation of the bolt 18.
A different, but equally unsatisfactory, arrangement is shown in FIG. 2. In this class of prior art, the lock cylinder 10 is mounted in a threaded housing 22 that has a flange 24 at the front and a nut 26 at the back. The cooperation of the front flange 24 with the nut 26 permits this lock cylinder housing to be secured to the face plate 14. However, the security of the lock rests entirely on the strength of the flange 24, and its engagement with the face plate adjacent thereto. By applying forceful hammer blows directly to the front face 29 of the lock cylinder 10, the flange 24 of the housing 22 can be broken off, or the face plate against which it is engaged can be deformed or broken, permitting the lock cylinder to driven into the locked housing, opening same.
In accordance with a preferred embodiment of the present invention, the foregoing and other drawbacks of the prior art are overcome, resulting in an lock mounting arrangement that is resistant to both prying and hammer attacks.
An illustrative embodiment includes a lock cylinder, a face plate, and a lock cylinder cover. Like the FIG. 1 prior art, the face plate forms a cavity into which the lock cylinder is positioned. The back of the face plate forms a frame covering the back of the lock cylinder. However, instead of covering the front opening with a swaged member, the cylinder is covered by a cover that includes at least one arm member passing through the face plate to the back. A fastener secures this arm against the back of the face plate. By this arrangement, the front cylinder cover is secured to the back of the face plate, preventing its removal by prying. The frame secures the cylinder to the rear, preventing it from being dislodged by hammer blows. Against all such attacks, the full structural integrity of the face plate serves to keep the lock cylinder in place and the lock secure.
The foregoing and additional features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.